Heretofore, solenoid actuated valves have used sensors to provide position feedback for control purposes. Linear variable displacement transducers (LVDTs) are well-known and widely used devices that measure the displacement of an armature relative to a coil assembly. One driving coil is used in conjunction with two secondary measurement coils.
Another type of sensor that has been used is a Hall-effect sensor. The Hall-effect sensor is an analog measuring device that provides a varying voltage output in relation to local disruptions of an electromagnetic field. The Hall-effect sensor typically is positioned to interact with a permanent magnet on the armature of the solenoid. The sensor and the magnet move relative to one another in order to vary the voltage output of the sensor thereby provide an indication of position. In a slide-by position sensor arrangement, tight control over the movement path of the armature usually must be maintained to ensure accurate displacement measurement.